Reversal Module LGB 55080

[Cliff George]

Sorry to throw a bucket of cold water on this stuff about reversing units but it seems to me (perhaps from my engineering background) fundamentally wrong to design something that is intended to detect something bad happening (a short circuit) and fix the problem before it becomes one. There is a lot of expensive electronics that theoretically could be damaged, wheels may become pitted. Actually the 'short circuit' solution doesn't work when more than one 'short circuit' reverser is used and different trains cross the boundary of each reverser at the same time (because each detects any shorts that occur and change polarity).
A better solution is to set up the correct polarity before entering or leaving and reversal section. This is actually what later designed reversers, such as the Massoth 8157001, can do.
Neither solution works when trains bridge both ends of a single reversing section at the same time.
I will now put on my hard hat and retire to a safe distance!

 

[Gizzy]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.

Do you need to rectify before the LEDs Steve?

The LED should light on the 'half wave' anyhow. The frequency of the pulses is so fast that no flickering will be detected by the human Mk 1 eyeball.

I have some garden lights which blew the filament lamps every week. The lamps were the same as the ones in my Mondeo sidelights, so I replaced these with LED versions. The low voltage supply is 12 V AC, but it didn't matter that the LED lamps were polarised and worked on a cars 12 V DC (you have to turn the lamp round if it doesn't light in a car as it can be fitted reverse polarity), and you don't see any flicker at 50 Hz.

Since fitting the LED lamps 2 years, I've not had a failure, and their high initial cost has easily been clawed back.

Also, I have an analogue Shoema Diesel that I fitted red/white bi coloured LEDs in the headlamps. These change according to the direction of travel. I used the LED as a diode as well as a lamp in a bridge configuration and it works fine on DC.

However, now that I'm DCC, the LEDS light up both red and white at the same time! I now underatand that this is because of the pulsed 'AC' signal from the MTS system. This 'anomaly' will soon be resolved though once I chip the loco.

 

[Gizzy]

Sorry to throw a bucket of cold water on this stuff about reversing units but it seems to me (perhaps from my engineering background) fundamentally wrong to design something that is intended to detect something bad happening (a short circuit) and fix the problem before it becomes one. There is a lot of expensive electronics that theoretically could be damaged, wheels may become pitted. Actually the 'short circuit' solution doesn't work when more than one 'short circuit' reverser is used and different trains cross the boundary of each reverser at the same time (because each detects any shorts that occur and change polarity).
A better solution is to set up the correct polarity before entering or leaving and reversal section. This is actually what later designed reversers, such as the Massoth 8157001, can do.
Neither solution works when trains bridge both ends of a single reversing section at the same time.
I will now put on my hard hat and retire to a safe distance!

Interesting comment Cliff.

I guess the LGB unit uses some sort of comparitor circuit to detect pulses, and if it detects a sudden pulse of the opposite polarity, it adds them together and thus cancels them out as they would be equal to zero. Thus there is no high transient spike which could damage the other electronics?

Many electronic and high power electrical devices have some sort of short protection. Power Generation springs to mind, as you have to match the phases between your differnce generators. We have such a system where I work. We get power from the National Grid but we have a Backup Diesel Generator if that fails. The circuitry is designed to keep the power on and match the phases, whilst the generator powers up....

 

[shropshire lad]

I had until recently an LGB reverse loop module running on short circuit mode and you could see a spark before switching when running in darkness on some of my locos. The unit doesn't protect from short circuits it requires them to switch. much better to use a Massoth unit with prediction tracks

 

[ntpntpntp]

Must admit I'm kind of with Cliff on this one - I'd rather the aproaching train was detected and the correct "polarity" preset before the train hits the reversing section's isolating joints, rather than relying on a fault condition to be detected. Especially in our large scale where several amps may be flow even if only for the briefest of moments. Remember the problems some folk have had with expensive MTS chips and boards being blown by shorts on Peco point frogs!

I have a solid-state reversing unit (a Tony's Trains module (made by NCE so matches my DCC system) that I bought from ebay "for the stores" ages ago. I've never yet used it.

There was quite a debate about a similar sort of thing a little while back on one of the DCC forums. There's an electronic module on the market called the "Hex Frog Juicer" that's intended to automatically switch "live frogs" on up to 6 points by detecting the short. It works well enough, but personally I'd rather use a micro-switch to change the frog polarity along with the point blades (as I've done with my live frog conversions of Peco and LGB R5 points)

 

[steve parberry]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.

Do you need to rectify before the LEDs Steve?

A bit light this Giz but please check you polarity as i cant remember exactly 8|

 

[Gizzy]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.

Do you need to rectify before the LEDs Steve?

A bit light this Giz but please check you polarity as i cant remember exactly 8|

I think you've drawn the LEDS the wrong way round, but I get the drift Steve....

 

[steve parberry]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.

Do you need to rectify before the LEDs Steve?

A bit light this Giz but please check you polarity as i cant remember exactly 8|

I think you've drawn the LEDS the wrong way round, but I get the drift Steve....

Now you have done by mentioning the D word

 

[Gizzy]

For me its just the bridge rectier and resistor feeding the power to the aux switch and then feeding the leds.

Do you need to rectify before the LEDs Steve?

A bit light this Giz but please check you polarity as i cant remember exactly 8|

I think you've drawn the LEDS the wrong way round, but I get the drift Steve....

Now you have done by mentioning the D word

I would do it like this?

No need for a bridge rectifier as the LED will work on AC, or rather the MTS signal from the track.

If the point is set against the route, a red aspect is shown.

I haven't included the bias resistors for the LEDS which I am assuming are built into the signal head

 

[muns]

I would stick a diode in "reverse parellel" to the LEDs in order to avoid back current issues.

Snd dont forget the current limiting resistor